Biomedical Engineering Reference
In-Depth Information
inside the cells upon 4 hours of incubation without effect on cell viability),
which presumably occurred through a passive ratchet diffusion.
67
As regards
this last aspect, the authors suggested cell mitosis as a contributing factor
for the nuclear internalisation: in fact in the last mitotic stage (telophase),
the nuclear membrane reformed, and hence it could have incorporated the
SWCNT-poly(rU) complex.
Finally, in another study, Silva
et al.
exploited the combination of CNTs
and RNA for a completely different purpose
68
: they demonstrated that
the treatment of SWCNTs with RNA helped stably suspend and purify un-
functionalised CNTs without the use of co-factors or surfactants. Even more
interesting, the authors also proved that the subsequent treatment of the
RNA-wrapped CNTs with the enzyme ribonuclease (RNase) very effectively
removed the “temporarily added” RNA, thus allowing for a complete recovery
of pure CNTs for further manipulations.
Taken together, all these indings concerning the interaction of CNTs with
nucleic acids seem very promising, as they combine crucial molecules in
biochemistry with nanotechnology, thus encouraging interesting applications
in biotechnology.
5.3 SENSORS AND NANOCOMPOSITES
Derivatised SWCNTs integrated into ield effect transistor (FET) circuits
(SWCNT-FETs) are attractive as electronic-readout molecular sensors
because of their fast response, high sensitivity and compatibility with dense
array fabrication.
69
Non-covalent functionalisation should be applied in order
to preserve the electronic properties of the device, especially in case of liquid
or gas-phase sensors. Regarding this last aspect, the molecular mechanism
that detects a particular odour is not known, but the response seems to be
speciic for the base sequence of the ssDNA), which has a high afinity for
SWCNTs. As a proof of that, Staii
et al.
70
used several odours to characterise
the sensor response, including methanol, propionic acid, trimethylamine
(TMA), dinitrotoluene (DNT, as liquid solution prepared by dissolving 50 mg/
mL of the material in dipropylene glycol) and dimethyl methylphosphonate
(DMMP). A small tank of saturated vapour of each odour was connected to
a peristaltic pump so that the low of air directed over the device could be
electrically diverted into one of the odour reservoirs for a set time (typically
50 s), after which the low reverted to plain air. In
Fig. 5.19
the authors
reported the signals before (blue points) and after (red points) coating with
ssDNA. In the presence of ssDNA adsorbed onto SWCNTs, DNT and DMMP
(which are agents simulating explosive vapour and nerve gas, respectively)
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